Question

我正在进行模拟，每次都会出错！我试过evreything但我找不到答案。这是代码： Person.java：

package School;

import java.util.Random;

public class Person {
    private Random rng;
    private String Name;
    private String[] Friends;
    private int Hobby;
    private boolean IsDitch;
    public Person(String Name, String[] Friends, int Hobby, boolean IsDitch){
        int aof = rng.nextInt(20);
        this.Name = Name;
        this.Friends = Friends;
        Friends = new String[aof];
        this.Hobby = Hobby;
        if(rng.nextInt(10) == 0){
            IsDitch = true;
        }else{
            IsDitch = false;
        }
        this.IsDitch = IsDitch;
    }

    public boolean getIsDitch(){
        return IsDitch;
    }

    public int getMaxFriends(){
        return Friends.length;
    }

    public String getName(){
        return Name;
    }
}

Interaction.java：

package School;

public class Interaction {
    public static void main(String[] args){
        String[] g;
        g = new String[2];
        g[0] = "Natasha";
        g[1] = "Fill";
        Person mrt = new Person("Adam",g,2,false);
        System.out.println(mrt.getName());
    }
}

我得到的错误：

Exception in thread "main" java.lang.NullPointerException
    at School.Person.<init>(Person.java:12)
    at School.Interaction.main(Interaction.java:9)

Answer 1

rng是null，您在实例化它之前在构造函数中使用它。

将其更改为：

rng = new Random();  
int aof = rng.nextInt(20);

您甚至可能希望rng静态，具体取决于您的确切需求。

Answer 2

我认为这是因为你没有初始化rng

编辑：oops太慢，但我同意peter.petrov

函数调用上的Java错误

2 个答案: